Sound picture film



May 7, 1940.

w.` l..A DAWSON SOUND PICTURE FILM F'iled- April 7, 1938 n 0 N N 2 0 ms Mm M i# m P n WD MA m ma. W mM L. /U\| .h W 8 C PT o n p am M 0W A mr E mw 2 Patented May 7, 1940 UNITED STATES PATENT OFFICE soUND PICTURE FILM` Wilf rid,L. Daws,on,fNew York, N. Y.,l assignor to BellTelephone Laboratories, Incorporated, New York, N. Y.,-a .corporation of New York Application April'v, 193s. serial No. 200,661 In GreatBritain October 6, 1937 3 claims'.

rlfhis invention relates to iilm sound recording systems in which one or morevolume control records are provided in addition to the main sound record. l

The object of the invention is the vprovision of one or more volume control records on a standard sound picture film without reducing the area of the picture, or the width of the film commonly used for the sound track.

A feature of the invention is the provision of one or more .volume control records placed between the sprocket holes of the lm.

In many known sound recording systems a control record is provided on the lin to control the volume of the reproduced sound. In the usual sound and picture film, the amount of space available for a control record is restricted, as most of the Vavailable space is required for the picture and the sound track. It is generally not practical to reduce the size of the picture or the widthof the sound track in order to accommodate the control record. For this reason the sound and picture films generally used in theatres have not been provided with any control records. As a result, the reproducing systems which involve the use of an auxiliary control record have not gone into general use.

According to the present invention, the control record is arranged to extend along the line of sprocket holes at the side of the iilm,so as to occupy the spaces between successivek sprocket holes.` The control record is preferably provided at the side of the film which bears the sound track, but if desired, one or more control records may be provided between thesprocket holes on both sides of the film, one or all of the' control records being utilized during the'reproduction of the sound. l

In the drawing:

Fig. l shows a variable density iilm sound record having variable density control records between the sprocket holes;

Fig. 2 shows a variable area film sound record having Variable area control records between the sprocket holes;

Fig. 3 .diagrammatically shows a lm sound recording system in accordance with the present invention; and

Fig. 4 diagrammatically shows a film sound reproducing system in accordance with the present invention.

The lm in Fig; 1 hasl a sequence of pictures l and a variable density sound record 2 located in the usual manner between the two rows of sprocket holes. Between the sprocket holes on one or both sides of the'film are one or more variable density control records 3, 4, 5 and 6.

Similarly, the film in Fig. 2 has a sequence of pictures i and a Variable area sound record 2 in the usual ylocation between the sprocket holes. "ff, Located between the sprocket holes on one or b'oth sides of the iilm are one or more variable area control records 3, 4, 5 and 6. Although variable density control rfecords have been shown associated with a variable density sound record and 1'() variable area control records have been shown associated with a' variable area sound record, it will be understood that the invention is in no Way limited to this particular arrangement, and that the variable area control records may be asso- 115 ciated with variable density sound records, or vice versa, or a variable area record may be used between one row'oi socket holes and a Variable density record between'the other row of socket holes on the same film.'r 20 In the recording system shown in Fig. 3, which is generally similar to'the system shown in U. Si. Patent 1,623,756, April 5v, 1927, C. F. Sacia, acoustic waves are detected by the microphone 1, arnpliiied by the amplifier 8 and transmitted through 2'5 the controlled amplifier 9 to the recorder l0 which produces a sound record inthe usual position on the lm Il. The sound recordV may be a single record, a multiple stereophonic record, a pushpull record or any other suitable type of record. 3f() Aportion of the output of the amplifier 8 is passed through an amplifier detector l2 to the recorder I3 which produces a control record between the sprocket holes of the film Il. A portion of theoutput. of' the amplifier detector I2 ',1 controls the amplication or transmission in the 'h' controlled'ampliiier 9 so as to partially or fully compress the range of amplitudes of the currents' supplied to recorder it). The controlled records may also be produced manually as shown in U. S. Patent 1,446,246, February 20, 1923, L. De Forest. In manual' control systems, the light valve or shutterv whichk records the control record may be operated by means of an auxiliary potentiometer in the signal current circuit. This may be arranged so that noA control track will be recorded when there is no volume compression in the main record. When abnormal sound levels are anticipated the attenuation of the potentiometer may be varied to reduce the amplitude ofthe 50 current supplied to the recorder Hi and simultaneoiisly a control track may be recorded of corresponding width or density. It may be desirable to have the portion of the control record corresponding to a given point on the main sound 55 record located on the film ahead of this point on the main sound record in order to compensate for the time of operation of the expanding device in the reproducing circuit.

In Fig. 4 light from the source I4 is projected through the sound record on the iilm II and a portion of the light deected by the prism I5 is projected through the control record on the film II. The light transmitted through the sound record on the lm II is detected by the photoelectric cell I6 and the sound modulated current amplified in the amplifiers I'I, IB and I9 and reproduced by the sound reproducer 20. The light transmitted through the control record on the film I I is detected by the photoelectric cell 2 I and the sound modulated current may pass through a controlling network 22 to an amplifier detector 23. The output of the amplifier detector 23 controls the amplification or transmission of the amplifier I8 to expand the volume range of the reproduced sounds to their original value before the currents are supplied to the reproducer 2li.v

The control of the sound reproducing apparatus by the volume control record, in which the recorded fluctuations corresponding to Volume changes are of relatively low periodicity as compared with the periodicity of the recorded sound currents in the main sound record, may be so effected, if desired, by the use of appropriate electrical filters in the controlling network, that the presence of the sprocket holes which Dass through the light medium for the control record at a constant speed of usually ninety-six sprocket holes per second, does not deleteriously affect the quality of the reproduced sound. These filters may be designed in accordance with the teaching of U. S. Patent 1,768,288, June 24, 1930, F. Mohr, with appropriate changes to adapt the filters for the slightly different conditions. The light beam used in reproducing the control record preferably has a greater height lengthwise of the lm than that normally used for the reproduction of a sound record and may, in fact, be high enough to cover the full height of a sprocket hole, or more, if desired. In place of a filter in the control network 22 a voltage limiting device may be used to limit the maximum voltage applied to the amplifier detector 23.

When recording the compression applied to a signal modulating current, the changes in the control record occur rather slowly, and if the volume of the sounds being recorded remains constant for any length of time the control record will be unchanged during that time. Thus, in a system as shown in U. S. Patent 1,623,756, the current reproduced from the control record has the characteristic of a slowly varying pulsating current and thus requires an amplifier detector capable of amplifying currents of very' low frequencies. Such amplifiers are difficult to construct and are notoriously unstable. In the present invention, the sprocket holes act as a light chopper producing a regular interruption of the reproduced currents at a frequency of ninety-six cycles per second so that the current supplied to the amplifier detector has the characteristic of a ninety-six cycle carrier current modulated in accordance with the changes in volume of the sounds. By suitable choice of the width of the scanning beam and the control network, the control current may be made nearly sinusoidal. Such a current may be easily amplied in a conventional alternating current amplifier.

The present invention enables the currents reproduced from the sound record to be adapted to the requirements of theatres of various sizes. For example, the sounds may be recorded with a moderate degree of compression so that the contrast in the sounds is about the same as now used, a control record made of the degree of compression applied to the recorded signal currents, and a separate control record of the location of the source of sound also placed on the record. In the smaller theatres the sound record only may be reproduced and will give a quality of sound and a range of volume comparable with the present method oi reproduction. In the larger theatres the sound record and the control record may be reproduced and the volume range of the reproduced signal currents expanded so as to produce a much wider range of volume in the reproduced sound than is now possible. Inthe more elaborate theatres, in addition to an expansion of the range of volume of the reproduced sound, another control record may operate upon the reproducing channel or channels so as to produce a stereophonic effect in the reproduction of the sound.

What is claimed is:

l. The method of reproducing a. sound film having a sound record on said film, and a control record within the strip of iilm occupied by the sprocket perforations which comprises reproducing said sound record as a sound current, amplifying and reproducing said current, scanning said control record with a beam of light, exciting a photosensitive device with the light modulated by said control record to produce a control current, modifying the Wave form of said control current to approximately sinusoidal form, amplifying and detecting said modified current, and controlling the transmission of said sound current by the products of said detection.

2. The method of reproducing a sound nlm having av sound record on said film and a control record within the strip of film occupied by the sprocket perforations which comprises reproducing said sound record as a sound current, amplifying and reproducing said current, scanning said control record with a beam of light, exciting a photosensitive device with the light modulated by said control record to produce a control current, limiting the maximum amplitude of said control current, amplifying and detecting said control current and controlling the transmission of said sound current by the products of said detection.

3. The method of reproducing a film having a sound record thereon and a control record within thestrip of lm occupied by the sprocket perforations which comprises reproducing said sound record as a sound current, amplifying and reproducing said current, scanning said control record with a beam of light having a height of the same order as the height of the perforations, excitingl a photosensitive device with the light modulated by said control record to produce a control current, modifying the wave form of said control current to approximately sinusoidal form, amplifying and detecting said modified current and controlling the transmission of said sound current by the products of said detection.

WILFRI'D L. DAWSON. 

